THE MARTIAN ATMOSPHERIC OXYGEN SURFACE SINK: A SOURCE FOR SUPER-RADICALS

摘要

Thermal loss processes of hydrogen and non-thermal atmospheric loss processes of hydrogen and oxygen and chemical weathering of oxygen with the surface soil influence the evolution of the Martian atmosphere with regard to its water inventory. These oxygen atoms that react with the surface soil are responsible for the toxicology of the Martian surface. Since the evolution of thermal and non-thermal escape processes, such as exospheric loss of oxygen via dissociative recombination, atmospheric sputtering and ion pick up depend on the history of the intensity of the solar EUV radiation and the solar wind density we use actual data from the Sun in time program for reconstructing the Sun's history of the spectral evolution from X-ray to EUV from the observation of solar proxies with different ages from the present up to 3.5 Gyr ago. Observations of flare activities of young solar-like stars inside these program strongly suggest that flare events are frequent and more powerful than observed at the present Sun. The high X-ray activity and the fast rotation of young solar-like stars indicate a much higher solar wind for the young Sun. We used a power law for the estimation of the average solar wind density of solar-like stars whose stellar winds were recently indirectly detected by using the amount of absorption in the HI areas as a diagnostic for their stellar mass loss rates. The correlation between mass loss and X-ray surface flux indicates a solar wind more than 1000 times massive in the distant past. We used a gas dynamic test particle model that involves the motion in the interplanetary electric and magnetic field for the estimation of the pick up ion loss rates which seem to be the most efficient non-thermal atmospheric loss process of the Martian atmosphere. By using new loss models and the data described above we estimate a loss of hydrogen and oxygen from Mars since 3.5 Gyr. We found that all non-thermal escape processes of oxygen from the present Martian atmosphere can not maintain the sum of thermal and non-thermal atmospheric loss rates of H in the ratio 2:1. Escape to space could therefore not be the only sink for oxygen on Mars since the desirable ratio of 2:1 of H:O loss rates should be established. Our study suggest that the missing oxygen needed for the validation of the 2:1 ratio between H and O is incorporated into the Martian surface by chemical weathering processes. The chemical environment, responsible for the oxidation of the Martian surface Mayers, is essentially also responsible for the toxicology of the Martian soil since the reactivity is related to ionized radicals. Our results have important implications for the search of organics on Mars and exobiology in general, as well as for electromagnetic subsurface sounding techniques.